A group could have the most number of players with the least number of active players. Do you still think they are the biggest?
Also, most players does not necessarily also mean most revenue. The players may not be depositing a lot..
If one group had 1000 players who all deposited 1000 each, thats $1,000,000.
If another group had 25000 players who all deposited 20 each, thats $500,000….
I still think your question needs clarifying…
You wont get anyone telling you who the biggest is in terms of most revenue because 1. they don’t want their competitors to know how much revenue they make, and 2. there is no real way of telling unless the competitors compared their revenue against each other, which is not going to happen..
If you wanted to base it on most players = most revenue… Well, Casino Rewards has 19 casinos and 5 poker rooms under their belt, meaning they have the most properties which should probably mean they have the most players and most revenue, right? 
But we will never know because we don’t go comparing our revenue against the others because the information is just not available..
Judy – most games – would have to be an MGS group, one that is running the new software. But in that case there are no single groups that are the largest because all of them running that software would have the same games.